Hyperswitch is a composable open-source payments infrastructure built in Rust that provides a modular platform for processing payments through multiple connectors. The system handles the complete payment lifecycle including authorization, capture, refunds, and dispute management, while offering features like intelligent routing, 3DS authentication, revenue recovery, and analytics. Built with a microservices architecture using Actix-web, it features a plugin-based connector system, event-driven design with Redis/Kafka, and comprehensive SDK support for web and mobile platforms. The codebase demonstrates strong engineering practices with typesafe ID generation, robust encryption utilities, and well-abstracted interfaces that promote reusability and maintainability.
Polar is an open-source, full-stack monetization platform designed for AI-era software developers. It serves as a Merchant of Record, handling checkout flows, subscriptions, usage-based billing, seats, discounts, and global tax compliance. The system is built as a monorepo with a Python/FastAPI backend (async SQLAlchemy, Dramatiq workers, PostgreSQL, Redis, Tinybird for event analytics), a Next.js web dashboard and customer portal, a React Native mobile app (Expo), a design system (Orbit), and multiple SDKs (TypeScript, Python) with a CLI tool. Architecture follows a service-oriented pattern with versioned REST APIs (2026-04, 2026-10, 2027-01), a repository pattern for persistence, benefit fulfillment strategies for integrations (Discord, GitHub, Slack, license keys), and framework adapters (Next.js, Nuxt, TanStack Start, Better Auth) for easy integration. The platform also includes an internal backoffice (HTMX/tagflow), observability (SLOs, invariants, Prometheus metrics), and merchant migration tooling from Stripe.